Yerkezhan Abikak

The growing demand for alumina, regional limitations in the availability of high-quality bauxite, and the accumulation of aluminum-bearing industrial residues have increased interest in alternative raw materials. In this review, we examine natural and technogenic non-bauxite aluminum-bearing resources, including nepheline ores, kaolin and kaolinitic clays, alunite ores, coal fly ash, and bauxite residue. Their geographical occurrence, chemical composition, aluminum content, major mineral phases, and associated valuable components are summarized and compared. Particular attention is paid to the mineralogical occurrence of aluminum, which largely determines the technological value of a resource. In nepheline ores, aluminum is incorporated into a stable framework aluminosilicate structure. Kaolinite is also relatively resistant, but its transformation into metakaolin substantially increases aluminum reactivity. Alunite represents a distinct sulfate-bearing resource that may provide aluminum together with potassium- and sulfur-containing products. In coal fly ash, aluminum is distributed between reactive amorphous aluminosilicate material and refractory mullite, whereas bauxite residue contains aluminum in several residual and secondary mineral phases associated with Fe, Ti, Si, Ca, and Na. Our comparison demonstrates that the suitability of alternative resources for alumina production cannot be evaluated from the total Al₂O₃ content alone: mineralogy, silica reactivity, impurity composition, resource availability, and the potential recovery of co-products must also be considered. Processing routes are therefore discussed in relation to the specific characteristics of each feedstock.

Carbonate thermochemical activation is a promising approach for modifying the mineralogical structure of nepheline–red mud mixtures prior to subsequent alkaline processing. However, quantitative statistical relationships between activation parameters and phase transformation remain insufficiently explored. In this study, Response Surface Methodology (RSM) combined with a Central Composite Design (CCD) was employed to develop and experimentally validate a quadratic regression model describing the influence of activation temperature, activation time, and NaHCO₃ concentration on cancrinite formation. Quantitatively determined cancrinite content obtained by X-ray diffraction (XRD) phase analysis was selected as the mineralogical response variable, enabling direct statistical evaluation of cancrinite-forming transformation. The developed quadratic model was statistically significant (F = 21.24, p < 0.0001) and explained 95.5% of the variability in the measured response (R² = 0.9550). Activation time exerted the strongest statistical influence on cancrinite formation, while activation temperature and NaHCO₃ concentration also showed statistically significant effects; the investigated interaction terms were not statistically significant. Numerical optimization identified a favorable region for cancrinite formation, with a predicted maximum response of 22.75 wt.%. Three independent validation experiments performed at practically selected operating conditions of 260 °C, 4 h, and 110 g/L NaHCO₃ yielded an average cancrinite content of 20.0 ± 1.0 wt.%. The principal novelty of the study lies in the use of quantitatively determined cancrinite content as the response variable in RSM, providing a direct statistical description of mineralogical transformation rather than optimization based solely on conventional technological responses. The developed model provides a quantitative framework for evaluating factor effects and identifying favorable activation conditions within the investigated experimental domain.

This study investigates graphene oxide/carboxymethyl cellulose composite membranes containing 3 wt.% graphene oxide. The influence of the carboxymethyl cellulose content on the structural organization, mechanical properties, electrical resistivity, and humidity-dependent conductivity was systematically analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, tensile testing, and electrical measurements. Fourier transform infrared spectroscopy indicated intermolecular interactions between graphene oxide and carboxymethyl cellulose functional groups. X-ray diffraction analysis showed gradual inter-layer expansion from 0.71 to 0.87 nm together with crystallite size reduction after polymer incorporation. Scanning electron microscopy observations demonstrated the increasing structural uniformity and polymer encapsulation of graphene oxide sheets with the increasing carboxymethyl cellulose content. Mechanical testing revealed improvement in the tensile strength from 6.6 to 17.8 MPa with the increasing carboxymethyl cellulose concentration. Simultaneously, the dry-state electrical resistivity increased from 5.8 × 10⁶ to 2.32 × 10⁷ Ω·m due to increasing dielectric separation between graphene oxide domains. Humidity-sensing experiments demonstrated reversible resistance changes in the 20–90% relative humidity range, associated with proton-assisted conduction through adsorbed water layers. The obtained results demonstrate that polymer incorporation strongly influences both the structural organization and electrophysical behavior of graphene oxide/carboxymethyl cellulose composite membranes.

The efficient processing of nepheline ores and red mud requires mineralogical preconditioning strategies that enhance aluminum recovery while controlling the potassium behavior in alkaline systems. In this study, carbonate–hydrothermal activation of a nepheline ore–red mud mixture (1:1 mass ratio) was investigated as a targeted approach for phase redistribution prior to alkaline leaching. Thermochemical activation in NaHCO₃ solution at 260 °C resulted in the partial destabilization of primary aluminosilicate phases and the formation of secondary carbonate-bearing and hydroxide phases. Quantitative phase analysis revealed the formation of cancrinite (~19 wt.%) and boehmite (~2.8 wt.%), indicating dissolution–reprecipitation processes accompanied by aluminum redistribution and carbonate incorporation. A two-stage alkaline leaching process with controlled calcium addition was applied to evaluate the effect of phase transformation on the extraction performance. The activated material exhibited enhanced reactivity, resulting in an alumina recovery of 92%–94% and selective potassium removal of 82%–87%. The results demonstrate that carbonate–hydrothermal activation acts as an effective mineralogical preconditioning strategy, transforming structurally stable aluminosilicates into more reactive phases. The proposed approach provides a basis for improving the efficiency and selectivity of integrated alumina recovery from complex aluminosilicate raw materials and industrial waste.

Chromite beneficiation tailings (CBTs) represent a significant environmental challenge, while simultaneously containing valuable metals that remain largely unrecovered. In this study, a sequential thermochemical–hydrometallurgical route was investigated for selective chromium extraction and the enrichment of platinum group metals (PGMs) from CBTs generated at the Donskoy Mining and Processing Plant. Alkaline sintering with Na₂CO₃ at 1000 °C followed by aqueous leaching enabled the transfer of up to 98%–99% of chromium into solution. The resulting residue was enriched in non-ferrous metals, rare earth elements, and PGMs. Subsequent sulfation roasting and water leaching promoted the dissolution of magnesium, nickel, and rare earth elements, while platinum and palladium remained predominantly in the solid phase, due to their low solubility under the applied conditions. Microstructural analysis using SEM–EPMA revealed that PGMs are selectively concentrated in Ni-bearing micro-inclusions, with local platinum content reaching up to 3.8 wt.% in Ni-rich regions. The proposed sequential processing strategy enables efficient chromium recovery and significant PGM enrichment in the residual phase, demonstrating the potential of CBTs as a secondary resource for integrated metal recovery.

This article provides a review of modern technologies for processing chromite ores and beneficiation wastes, with a focus on the recovery of magnesium and platinum-group metals (PGMs). It reveals that the traditional use of chromites solely as a source of chromium limits the potential of this raw material, whereas comprehensive processing enables the recovery of associated components, including serpentine minerals, which are widely present in chromite ores and tailings. Pyrometallurgical, hydrometallurgical, plasma-arc, and biotechnological methods are examined, as well as their integration into combined flowsheets. Particular attention is given to sulfation, chloridization, and carbochlorination processes, which ensure a high degree of PGM recovery. Economic and environmental aspects of comprehensive processing are discussed, including carbon footprint reduction, waste minimization, and prospects for the development of “green metallurgy.” It is concluded that the further advancement of resource-efficient and environmentally safe technologies for chromite processing will increase production efficiency, ensure resource independence, and support compliance with global carbon neutrality requirements.

This study investigates the use of preliminary thermochemical activation in a NaHCO₃ solution under elevated pressure and temperature to modify the chemically stable and hard-to-process phase composition of various mineral raw materials and improve the recovery of valuable components. The method was tested on various types of mineral raw materials, including slag from the reductive smelting of red mud from alumina production prior to acid leaching, ash before chemical beneficiation, gibbsite–kaolinite bauxite prior to gravity separation, and nephelines, for which the sintering process was replaced with chemical beneficiation. The slag from the reductive smelting of red mud was also tested before acid leaching. The activation of slag enhanced tricalcium silicate formation lead to leaching recoveries of ~96% for rare earth elements, ~92% for TiO₂, ~98% for CaO and Al₂O₃, and 50% for Fe₂O₃, compared to much lower values without activation. With ash, activation eliminated the sillimanite and hedenbergite phases, increased mullite and free silica, and formed calcite, resulting in a 15–20% higher silica recovery. With gibbsite–kaolinite bauxite, activation altered kaolinite, siderite, quartz, and hematite contents; eliminated calcium silicate; and improved the silicon modulus of the sand fraction by 35.9% during gravity beneficiation. For nepheline ore, activation promoted the formation of albite and hydrosodalite, eliminated corundum and andradite, and increased silica recovery from 33.58% to 59.6%. These results demonstrate that thermochemical activation effectively transforms mineral structures and significantly improves the efficiency of subsequent beneficiation processes.

Red mud from bauxite processing is among the large-tonnage technogenic waste that poses a significant ecological threat. At the same time, red mud serves as a raw material source for expanding the resource base for obtaining iron, rare metals, and rare earth elements. Numerous studies on their utilization have shown that only through comprehensive processing, combining pyrometallurgical and hydrometallurgical methods, is it possible to maximize the extraction of all the useful components. This work addresses the first stage of a comprehensive technology for processing red mud through reduction smelting, separating iron in the form of pig iron, and producing slag. Studies were conducted on the reductive smelting of red mud using waste slurry from alumina production as the calcium-containing material, taken in proportions calculated to obtain a fluid slag with a hydraulic modulus of 0.55–0.8. The permissible mixing range of red mud with waste slurry was determined to be in the ratio of 0.56–1.2. In cases where the charge was prepared in violation of the required hydraulic modulus value, pig iron was not obtained during smelting. When the hydraulic modulus requirement was met, the temperature of the reductive smelting process was 1350–1400 °C. The total amount of recovered iron obtained as pig iron and fine fractions amounted to 99.5% of the original content. The low iron content (0.23–0.31%) in the non-magnetic slag fraction allows for the production of high-quality titanium oxide and rare earth element concentrates in the subsequent stages of the comprehensive hydrometallurgical processing of red mud, involving acid leaching. Based on the results of a phase analysis of the slag, pig iron, and melt, the reactions of the reductive smelting process were established, and their thermodynamic likelihood was determined. In fluid slags, the content of the sodium aluminosilicate phase is twice as high as that in slag with a higher hydraulic modulus. The reductive smelting of 100% red mud with the addition of calcium oxide, calculated to achieve a hydraulic module of 0.55 at a temperature of 1350–1400 °C, produced pig iron and slag with high alkali and iron contents.

This study focuses on optimizing the alkali roasting conditions for chromite beneficiation tailings with the goal of enhancing chromium oxide (Cr₂O₃) extraction. Within the experimental framework, the variables included roasting temperature, the amount of added Na₂CO₃, and reaction time. The results revealed that temperature is the most critical factor directly affecting the extraction efficiency. Increasing the amount of Na₂CO₃ contributed to an increase in Cr₂O₃ recovery, although excessive addition may not be economically justified. The optimal conditions—1000 °C, 120%–130% Na₂CO₃ (relative to tailings mass), and 120 min—enabled a Cr₂O₃ extraction rate of up to 98.6% through aqueous leaching. The phase transformation analysis confirmed the breakdown of the spinel structure and formation of water-soluble sodium chromate. Microanalysis observations and measurements validated the progressive destruction of chromite grains and sodium enrichment in the reaction zones. The remaining leaching residue consisted of inert Na₂Mg₂Si₂O₇ and MgO, suitable for further metal recovery. The proposed approach enables efficient detoxification of hazardous tailings and serves as a basis for integrated utilization of Cr-bearing industrial waste.

The cyanidation of precious metals from ores and secondary resources has been classified as a hazardous process due to the release of toxic gases. The use of environmentally friendly and cost-effective processes is a suitable alternative to cyanidation. Thiourea leaching has been shown to be one of the best alternative reagents to cyanide. The present work aims to evaluate the efficiency of the thiourea leaching of gold and silver from pretreated pyrite cinders. The use of pre-chemical activation prior to leaching helped to increase the amount of free gold and silver particles. A preliminary leaching test led to the selection of Fe₂(SO₄)₃ as a suitable oxidizing agent for Au and Ag leaching. To select suitable leaching parameters, the response surface methodology (RSM) was used to optimize some parameters that can considerably affect sulfuric acid–thiourea leaching and identify the greatest interaction between them. The optimized parameters of 30 g/L thiourea, 10% pulp density, pH = 1, and 50 °C over 4 h of leaching time allowed for Au and Ag recoveries of 98.31 and 88.57%, respectively.